Purity, formulations and chromatography

The idea

In chemistry a pure substance is a single element or compound; it melts and boils at specific temperatures, while impure substances melt over a range. A formulation is a mixture designed as a useful product, such as paint or medicine. In paper chromatography, substances separate as the solvent moves up the paper. Rf = distance moved by substance ÷ distance moved by solvent. A pure substance gives one spot.

1. Draw the start line in pencil above the solvent.
2. Measure both distances from the start line.
3. Compare Rf values with known substances run in the same solvent.

Watch out Draw the start line in pencil: ink would dissolve and run.